Balloon dilatation catheters are used for a variety of medical procedures, including dilation of obstructed body lumens, such as blood vessels, coronary arteries and the esophageal tract. In particular, such catheters are used in angioplasty procedures to enlarge the lumen of a blood vessel which is constricted or stenosed by arteriosclerosis.
In a type of angioplasty known as percutaneous transluminal coronary angioplasty (PTCA), dilatation catheters are used in conjunction with a guide catheter through which the dilatation catheter is inserted and guided to the desired location in the body lumen. In a typical PTCA procedure, the guide catheter is percutaneously introduced into the patient's arterial system and is fluoroscopically guided to the entrance to the coronary artery. A dilatation catheter, having a balloon at its distal end, then is passed through the guide catheter, so that the balloon extends beyond the distal end of the guide catheter into the coronary artery. The catheter then is manipulated to place the balloon (deflated) into the obstruction. Once the balloon is placed within the obstruction, it is inflated to dilate the obstructed lumen.
The balloon of the dilatation catheter must be deflated to a low profile in order for it to be passed through the guide catheter and, more particularly, through the stenosis. The balloon is deflated by applying negative pressure to the balloon through an inflation/deflation lumen that extends from the proximal end of the catheter to the interior of the balloon. The configuration assumed by the balloon upon deflation presents a problem in catheter utilization. Typically, the balloon forms a pair of opposed, radially-extending, flat wings, when collapsed under the influence of negative pressure, as shown in FIG. 2. To insert the balloon into the lumen of a guide catheter, the physician must manually wrap the wings about the catheter shaft prior to insertion into the guide catheter. The reduced profile of the balloon, caused by the wrapping, facilitates insertion of the balloon into the guide catheter and the obstruction. However, after the balloon has been inflated in the patient and it is desired to recollapse the balloon, the balloon will again tend to assume the two wing configuration. The radial extent of the opposed wings may make it difficult for the balloon to refold as it is withdrawn into the guide catheter or if it is desired to recollapse the balloon and advance it to another stenosed location. In the latter case, the radial extending wings may make it more difficult for the balloon to be inserted into the stenosis.
A desirable feature of a balloon dilatation catheter, therefore, is a balloon which has a reduced profile to facilitate insertion into a guide catheter and a vascular stenosis, without the need to manually wrap the balloon about the catheter shaft.
The foregoing problem has not gone unrecognized as evidenced by proposed devices to provide a means for causing a dilatation balloon to be wrapped closely about a catheter shaft to form a reduced profile. For example, see U.S. Pat. No. 4,292,974, issued to Fogerty. Notwithstanding such proposals, there remains a need for a simple effective means to facilitate collapse of a dilatation balloon to a low profile.
A further problem encountered in using dilatation balloon catheters is the failure of the balloon to deflate, following dilatation of the obstruction. Because of a malfunction in the catheter itself, the dilatation balloon may fail to deflate when aspirated. In these instances, the balloon must be intentionally destroyed before withdrawal through the guide catheter. The balloon is destroyed by inflating the balloon to a pressure at which the balloon wall ruptures or bursts. Unfortunately, many current dilatation balloons have burst pressures which exceed the delivery capabilities of most clinical inflation devices, often requiring burst pressures in excess of 20 Bars. Such pressure may rupture the body lumen as well as the dilatation balloon, thereby creating an undesirable hazard to the patient. A further desirable feature of a dilatation catheter, therefore, is to provide a balloon having an artificially lower burst pressure to facilitate easy destruction of the balloon, if necessary.